The invention relates to a light emission unit for emitting plural linear light beams of different color, which has a plurality of light emission element arrays for emitting a linear light beam of same color.
A color printer for recording a full-color image to an instant photo film as a recording material is disclosed in JPA No. 11-377442 and so forth. The color printer has an exposure head for emitting red, green and blue recording light beams toward the instant photo film. The exposure head includes red, green and blue light emission element arrays, each of which has a plurality of light emission elements arranged linearly along the direction perpendicular to the feeding direction of the instant photo film. By use of this exposure head, three color synchronous recording or three color line sequential recording is carried out for recording a full-color image. As the light emission element, an organic light emission element may be used as well as a light emitting diode (LED). The organic light emission element is well-known by xe2x80x9cSeparate Volume of November issue of The Monthly Display (published by TECHNO TIMES CO., LTD.)xe2x80x9d and so forth.
The organic light emission element has a transparent substrate and a dielectric mirror, transparent positive electrode, at least one organic compound layer, and a negative electrode which are stacked on the transparent substrate in this order listed. Recording light beams, generated in the organic compound layer, are reflected by the negative electrode, so the light beams are emanated from the transparent substrate through the positive electrode. In the organic light emission element, recording light beams are resonated in a micro cavity between the dielectric mirror and the negative electrode, so it is possible to have bright light, the half width of the spectrum of which is extremely narrow.
For three color synchronous recording or three color line sequential recording by use of the organic light emission elements, red, green and blue light emission element arrays are arranged parallel to one another. In respective light emission element arrays, a plurality of organic light emission elements for emitting light beam of same color for each pixel are arranged in line.
In front of the light emission element arrays is disposed a focusing lens array, which is comprised of a plurality of microscopic focusing lens arranged in line. Recording light beams from the light emission element arrays are focused on the instant photo film through the focusing lens. The focusing lens may be configured such that linear recording light beams of three color are focused on the same line of the instant film, or on different lines that are parallel to one another.
The light emission element arrays of LED type is configured by mounting LED arrays of three-color on a substrate. Each LED array has a plurality of LEDs for emitting recording light beams of same color arranged in line. Recording light beams from the LED array are focused on the instant film through the focusing lens array in the same way as above.
In order to keep the light emission surface from a dust or flaw, it is preferable to secure a transparent cover plate on the light emission surface. The light emission element arrays and the cover plate, which comprise a light emission array unit, and the focusing lens array are incorporated in the exposure head.
For effective utilization of recording light beams, the incident surface of the focusing lens array is required to be located close to the light emission element array, such that the angular aperture is increased. However, the transparent substrate and the cover plate are provided between the light emission element array and the focusing lens array. Thus, because of the difficulty to shorten the distance between the incident surface and the emission surface, it is hard to increase utilization efficiency of the emitted light beams from the light emission element arrays.
In order to utilize recording light beams, a condenser lens array can be disposed between the light emission array unit and the focusing lens array. In that case, however, parts number of the exposure head is increased for providing the condenser lens array, so manufacturing cost is also increased. Furthermore, in order to adjust the optical axis of each condenser lens so as not to be inclined against to the optical axis of corresponding focusing lens, the condenser lens array must be positioned with high accuracy. This increases the manufacturing cost of the exposure head.
The present invention is to provide a light emission unit for emitting linear light beams of full-color, in which a focusing lens array is disposed close to an emission surface of light emission element arrays without increasing manufacturing cost.
To achieve the above objects, a light emission unit of the present invention comprises a plurality of light emission element arrays for emitting a plurality of linear light beams of different color from a light emitting surface, a transparent plate for protecting the light emitting surface, and a plurality of lens arrays integrated with the transparent plate such that each of the lens arrays corresponds to each of the light emission element arrays. Each of the light emission arrays includes a plurality of light emission elements arranged in line for emitting light beam of same color. In addition, respective lens array includes a plurality of condenser lenses faced to respective light emission elements.
In the embodiment, the light emission unit is used for printer for exposing an image to a photosensitive material. The light emission element array includes a transparent positive electrode, an organic compound layer, a negative electrode, which are stacked on the transparent layer in this order listed. The organic compound layer includes organic light emission element arrays for red, green and blue for emitting linear light beam of red, green and blue respectively.
The radius of curvature of the condenser lens becomes smaller as the wavelength of light beam of corresponding light emission element becomes longer, such that red, green and blue light beams are focused on the photosensitive material without causing axial chromatic aberration. The light emission element arrays of red, green and blue are arranged in this order. The condenser lenses for red band blue are located such that their optical axes are not coincident with optical axes of corresponding light emission elements, but slightly shifted toward the condenser lens for green. Thereby, red and blue light beams are inclined toward the green light beam, such that linear light beams of three color are focused on the same line of the photosensitive material.